Description

Sandbox escape due to use-after-free in the Widget: Gtk component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.6",
  "pubDate": "2026-09-29T13:17:47.037Z",
  "pubdate": "2026-09-29T13:17:47.037Z",
  "executiveSummary": "A critical use-after-free (UAF) vulnerability has been identified within the Gtk widget component of Firefox, facilitating a sandbox escape.\nThis vulnerability allows an attacker to manipulate memory management processes within the browser's rendering engine, potentially leading to arbitrary code execution outside the confines of the restricted security sandbox.\nThe vulnerability affects Firefox 157, Firefox ESR 153.4, and Firefox ESR 140.17.\nExploitation requires the attacker to influence the lifecycle of Gtk-related objects, likely through crafted web content designed to trigger memory corruption.\nThe risk implication is severe, as a successful sandbox escape permits an attacker to bypass the browser's primary defense mechanism, enabling full system compromise or persistence on the underlying host operating system.\nSuccessful exploitation generally requires the victim to interact with malicious content, leveraging browser memory management flaws to achieve a state where a dangling pointer is referenced after the associated object has been deallocated.\nThe vulnerability underscores the risks inherent in complex UI integration layers where widget event handling and asynchronous object destruction may lead to race conditions or improper state management.",
  "technicalDetails": "The vulnerability originates within the Gtk integration layer of the Firefox browser, specifically involving the management of Gtk widgets. Use-after-free (UAF) conditions in this context occur when a Gtk object is deallocated or destroyed while the browser's rendering engine or event handling loop retains a dangling pointer to the memory address previously occupied by that object.\nIn the Gtk framework, objects rely on reference counting or specific destruction signals. If the Gtk widget lifecycle is not strictly synchronized with the Firefox memory management system, a scenario arises where the browser triggers an operation on an object that the underlying Gtk implementation has already disposed of.\nThe attack flow typically initiates by forcing the browser to create and subsequently discard specific Gtk-based UI elements. An attacker can use techniques such as heap spraying or precise heap grooming to occupy the memory region previously held by the freed object with attacker-controlled data.\nOnce the dangling pointer is dereferenced during a subsequent event or widget update, the browser operates on the attacker-controlled data instead of the original object structure. If this data is formatted to simulate a legitimate Gtk widget structure, the attacker can hijack the control flow of the browser process.\nBy manipulating vtable pointers or callback functions embedded within the forged object, the attacker can redirect execution to arbitrary code. Given that this interaction happens within the Gtk layer, it creates a pathway to escape the lower-privileged content process sandbox, granting the attacker the privileges of the browser's parent process.\nThis vulnerability is particularly dangerous because it bypasses conventional browser security boundaries by exploiting the interface between cross-platform rendering code and the native Gtk library. The complexity of Gtk event propagation and its interaction with the browser's multi-process architecture provides a wide surface for triggering these memory management inconsistencies.\nThe remediation involves correcting the object reference lifecycle to ensure that no browser components maintain references to Gtk widgets post-destruction, typically implemented via robust smart pointer usage or explicit nullification of pointers upon object destruction events. The affected versions include Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17."
}